As electronic devices become smaller and operate at higher speed, energy emitted in the form of heat increases dramatically. Thermal interface materials are commonly used in such devices to transfer the excess heat dissipated across physical interfaces. Most common types of thermal interface materials are thermal greases, phase change materials, and elastomer tapes. Thermal greases or phase change materials have lower thermal resistance than elastomer tapes because of the ability to be spread in very thin layers and provide intimate contact between adjacent surfaces. Typical thermal impedance values range between 0.6-1.6xc2x0 C./cm2/W. However, a serious drawback of these types of materials is that thermal performance deteriorates significantly after power cycling, or after thermal cycling, such as from xe2x88x9265xc2x0 C. to 150xc2x0 C., when used in VLSI chips. It has also been found that the interface materials have the tendency to be pumped or squeezed out of these mating surfaces when subjected to tests or in use.
The present invention proves a thermal interface material that is particularly suitable for use as interface material in electronic devices. The improvements over existing materials include: ease of handling, improved reliability and higher thermal conductivity.
The invention is directed to an interface material composition that comprises a rubber, such as a saturated or unsaturated hydrocarbon rubber, a phase change material, such as paraffin waxes, including malenized paraffin waxes, or polymer waxes, and at least one thermally conductive filler. The thermally conductive filler advantageously comprises particles of materials of high thermal conductivity and, preferably, dispersed in the phase change material.
The hydrocarbon rubber may comprise at least one saturated or unsaturated olefin rubber, an hydroxyl terminated rubber or mixtures thereof. Hydrocarbon rubber may comprise saturated rubber from the group ethylene-propylene, polyethylene/butylene, polyethylene-butylene-styrene, polyethylene-propylene-styrene, and hydrogenated polyisoprene. Unsaturated rubbers may comprise polybutadiene, polyisoprene, polystyrene-butadiene.
The phase change material may comprise a paraffin wax having a melting point in the range of about 20xc2x0 C. to 100xc2x0 C. Alternatively, the phase change material may comprise a polymer wax having a melting point in the range 40xc2x0 C. to 160xc2x0 C. Paraffin waxes may comprise a mixture of solid hydrocarbons having the general formula CnH2n+2.
Desirable fillers for the composition include silver, aluminum, copper, and alloys thereof; boron nitride, aluminum nitride, silver coated copper, silver coated aluminum, carbon fiber, metal coated carbon fiber, and nickel coated fiber. It is presently preferred to employ a filler comprising at least 20% by weight boron nitride or a filler comprising at least 50% by weight of silver, copper and/or aluminum.
It also contemplated to include a functional organic-metallic coupling agent to facilitate dispersion of the filler and an antioxidant may be added to inhibit oxidation and thermal degradation of the phase change material. It is preferable to include thermally conductive filler particles in the range of about 0.5-25 xcexcm with a maximum particle size of about 100 xcexcm.
Additionally, another aspect of the invention is an interface composition material, as described, on a carrier which may be in the form of a tape.